The present claimed invention relates to the field of digital communications. Specifically, the present claimed invention relates to an apparatus and a method for adaptively selecting a soft symbol for a subsequent operation, e.g., decoding, within a communication device.
Wireless communication is expanding to all forms of devices that use information, e.g. cellular phones, a networks, personal digital assistants (PDAs), digital cameras, etc. One form of wireless communication, known as Code Division Multiple Access (CDMA) spread spectrum format, is among the most commonly deployed wireless technology. Because of increasing demand and limited resources, a need arises to improve their fidelity and performance of wireless communication devices and systems.
Referring to prior art FIG. 1, a conventional base station 104, e.g. cell, and a mobile unit 102, e.g. a cell phone, are shown. A CDMA system uses a common bandwidth to transmit the pilot signal and a data signal 106 between a base station 104 and a mobile unit 102, for multiple users. Hence, the bandwidth is occupied by an combination of many signals. Furthermore, the original signal can take multiple paths to arrive at a destination device with various forms of delay and phase shift. These signals from the different paths are referred to as multipath signals. Because the multipath signals can vary substantially in signal strength and other performance factors, a need arises for a method to appropriately evaluate received signals for processing into meaningful data, e.g., voice data.
One conventional configuration identifies only a fixed location, or portion, of bits of the combined signal for subsequent decoding. Often, the fixed location of bits from the combined signal is chosen for its overall performance in many different signal-reception scenarios. Unfortunately, this prior art configuration typically yields only nominal performance in each of the wide-range of reception scenarios. Furthermore, this fixed portion of the combined signal is typically identified in a design phase of the hardware and software, and then programmed into the phone. Hence, a phone may be limited during its entire life to the fixed portion of the combined signal. Consequently, a need arises for a method that overcomes the prior art limitations of selecting a fixed location of bits from the combined signal for decoding.
In summary, a need arises to improve their fidelity and performance of wireless communication devices and systems. Furthermore, a need arises for a method to appropriately evaluate received signals for processing into meaningful data, e.g., voice data. Finally, a need arises for a method that overcomes the prior art limitations associated with selecting a fixed location of bits from the combined signal for decoding.
The present invention provides a method and apparatus for improving the fidelity and performance of digital communication devices and systems. In particular, the present invention provides a method to appropriately evaluate received signals for processing into meaningful data, e.g., voice data. Finally, the present invention provides a method that overcomes the prior art limitations associated with selecting a fixed location of bits from the combined signal for a subsequent operation.
Specifically, one embodiment of the present invention provides a method of adaptively selecting a soft symbol for a subsequent operation in a communication device is disclosed. In one embodiment, a signal is received at the communication device. Next, the signal is demodulated. Then, a strength level, such as a signal to noise ratio Eb/Nt, is determined. Based upon the strength level determined for the signal, a location, or a consecutive sequence, of bits from the signal is determined in the final step for a subsequent operation. The strength level and the location of bits is adaptively updated for the signal over time. It is appreciated that Eb/Nt is the ratio of combined energy per bit to the effective noise power spectral density, which is known by those skilled in the art.
In another embodiment of the present invention, the aforementioned method is implemented in a communication device having a processor, e.g., a general purpose processor, a memory, a rake receiver, and a digital signal processor (DSP). Specifically, the memory portion of the communication device contains data and program instructions that, when executed via the processors, implement the aforementioned method for adaptively selecting a soft symbol from the composite signal for a subsequent operation in the communication device. This bit selection process provides very little head room. This scheme forces higher resolution in the area around the origin, and saturates large signal amplitudes. The process is viable because, at large amplitudes, the signal is unlikely to be decoded incorrectly, and thus does not require much resolution at these signal amplitudes.
These and other objects and advantages of the present invention will become apparent to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various drawing figures.